Electromechanical amplifier



2 Shuts-Shoot 1 Filed Nov. 29, 1943 INVENTOR. MARC '4. M71 AWDE Nov. 30,1948. M. A. LALANDE ELECTROIECHANICAL AMPLIFIER 2 Sheets-Sheet 2 FiledNov. 29. 1943 IN VEN TOR. M14196 4. L fll flNDE Patented Nov. 30, 1948ELECTROMECHANICAL AMPLIFIER Marc A. Lalande, Lyon, France, assignor toInternational Standard Electric Corporation, New York, N. Y., acorporation of Delaware Application November 29, 1943, Serial No.512,123 In France March 23, 1940 3 Claims.

The present invention relates to electro-mechanical amplifier devices,particularly as used for the amplification of telephone communicationcurrents and the like.

According to one embodiment of this invention, use is made of anelectro-mechanical amplifier element, comprising a receiver which isacoustically coupled to a carbon granule microphone, while both are keptin an atmosphere of a gas, which latter is preferably one which is agood conductor of heat. The amplifier element is mounted on a support orbase similar to a tube base, and can be used in telephone repeatercircuits of the two-wire amplifier type, either series-connected on aline or as a receiving amplifier in connection with a telephone stationor a telephone receiver. The amplifier assembly, including the source ofenergy, can be constructed as a compact piece of apparatus that iseasily transportable and that can be conveniently connected with anordinary telephone station.

The invention is hereinafter explained with reference to the appendeddrawings, in which:

Fig. 1 shows, in section, an amplifier element according to thisinvention;

Fig. 2 illustrates one example of this invention as applied to a two-wayrepeater; and

Fig. 3 illustrates a capacity shifting plug for use in the circuit ofFig. 2.

Referring to Fig. 1, the amplifier element properly so-called, shown atI, is screwed and soldered on a support 2 which is sustained byinsulating members 3. A metallic housing 4 fits snugly on a support 5,e. g. of brass, to which it is soldered as well, in order to insuretightness. The member 5 maintains in position the insulating members 3which are perforated and are traversed by tubular members 5 havingtapered lower ends. Glass tubes 6' are positioned within the tubularmembars 5 and protrude slightly from the ends of the members 6 wherethey are fused to the ends of the members forming glass heads I. Theconductors for afiording external connection pass through some of theselittle tubular members toward the amplifier element I, traversing theglass beads l in such a way as to form a gas-tight connection. Referencecharacter 8 denotes a copper pipe which passes all the way throughmember 5, to which it is soldered, and which serves to allow evacuationand afterwards serves for introducing r a selected gas. This tube issealed off and soldered together at 9, after the gas has been introducedtherethrough. The use of gas is necessary on account of acousticcoupling that exists thereby, between the receiver and the microphoneunits of the amplifier, which units may all be types described in FrenchPatent 731,715, filed February 22, 1932. Furthermore, the gas pressuremay be different from the atmospheric pressure, depending on thecharacteristics of the amplifier ele ments. Finally, member 4 is closedat the lower end by a base plate ID, on which the pins H are fastened,which permits insertion of the amplifier into a conventional tubesocket, e. g. one of the socalled Octal type,

The reason for using a gas diflerent from air is, on the one hand toprotect the amplifier against the hygroscopic efl'ects due to thehumidity of the air, and on the other hand to prevent oxidation of thecarbon by the oxygen of the air and to facilitate the acoustic couplingbetween the receiver and the microphone of the amplifier element. Asmentioned above, it is usually preferable to make use of a gas that is agood conductor of heat, in order to permit the carbon granules which areslightly heated by the passage of the current to dissipate the heat, e.g. to use hydrogen.

Amplifier elements constructed in this way are easily interchangeableand may be used in a certain number of circuits of which there is heregiven one example.

Fig. 2 illustrates one example of a circuit in which theelectromechanical amplifier of this invention is used for theamplification of a twowire telephone circuit at an intermediary point.

The circuit is that of a characteristic repeater; 2| and 22 designatethe differential transformers and the balancers consist of an adjustableresistance, 23 in series with a capacity. The resistance is variable,and the capacity may consist of an assembly comprising three condensers,24 and 25, of 1 microfarad and 26, of 0.25 microfarad, which can beunited in various ways by means of the switching system 21. Thisswitching device consists of six receptor contacts disposed in hexagonalform and a four-pin plug, 21' this latter being connected as shown inFig. 3. By successively shifting this plug by rotation of degrees, it ispossible to obtain the following various connections: open circuit,short circuit, 2 mt. (condensers 24 and 25 in parallel), 1 mi, 0.5 mi.(condensers 24 and 25 in series) and 0.25 mi.

The midpoints of the diilerential transformers 2| and 22 are connectedover a low-pass filter device 29 which allows the passage of ringingcurrents of low periodicity, such as 20 cycles.

The secondary of the diflerential transformer 2| is connected to theelectro-mechanical amplifier element 3| over a gain adjustmentpotentiometer 30. The feeding of the electro-mechanical amplificationbuttons is effected by a. battery 2 over de-coupling resistances 33 and34 pro with condensers 35 and 36, and a switch or key 39 serves forstarting in operation. A gain correcting circuit is provided at 31 andan output transformer at 38. Amplification in the other direction oftransmission is eflected by similar elements, which is thoughtunnecessary to describe in detail.

This amplifier device can be constructed so as to be portable and it canrender great service in every case, e. g. in the country, where thereare no electrical energy supply sources available or when it isimpossible to use bulky equipment. It can be made up to fit in a box 15by 10 by 15 cm., for examplev Although this invention has been describedin one embodiment and with the above described examples of utilizationcircuit, it is evident that the invention is by no means limited to suchexamples but that it is capable of numerous variations and modificationssuch as will be apparent to those skilled in the art without departingfrom the scope of the hereunto appended claims.

What is claimed is:

1. An electro-mechanical telephone amplifier unit comprising, a cup-likemetal shell having a cylindrical side wall terminating at one end in acircular opening, a base plate covering and sealing said opening, aplurality of insulated connector pins rigidly mounted on said base plateand projecting away from said shell, a metal partition dividing thespace within said shell into a base compartment adjacent said base plateand a working compartment remote from said base plate, insulating meansmounted on said partition within said working compartment, anelectro-mechanical telephone amplifier unit of the acoustically coupledtype positioned within said work compartment and supported on saidinsulating means out of direct contact with said shell, a plurality oflead wires extending through said partition and said base compartmentand electrically insulated from each other and connected to saidconnector pins to provide electrical connections to said amplifier unit,and a body of gas filling said working chamber and surrounding saidamplifier unit to provide the acoustical coupling for said amplifierunit, said gas having a high thermal conductivity as compared with airwhereby the heat produced by the operation of said amplifier unit istransmitted emciently to the surrounding metal walls 01 said shell withthe result that the heat is dissipated rapidly and at a steady rate.

4 2. Apparatus as described in claim 1 wherein said gas is hydrogen andwherein an evacuation and gas filling tube extends from said workingcompartment through said partition to said base plate whereby theworking compartment may be evacuated and filled with hydrogen.

3. An electro-mechanical telephone amplifier comprising, a thin metalcup having a substantially cylindrical side wall closed at one end andopen at the other end, a base plate of insulating material snuglyfitting and sealing the open end of said cup, a plurality of insulatedconnector pins rigidly mounted in predetermined spaced relationship onsaid base plate and projecting away from said cup, a gas-tight metalpartition extending across said cup transversely of the axis thereof andforming a sealed chamber which is bounded by the side and end walls ofsaid cup and said partition, an electro-mechanical telephone amplifierunit of the acoustically coupled type positioned within said chamber andmounted by an insulated bracket means on said partition and out ofdirect contact with said cup, and means providing a plurality ofinsulated electrical connections through said partition and respectivelyto said connector pins and providing electrical connections to saidamplifier unit, said sealed chamber being adapted to be filled with agas having high thermal conductivity with respect to air, whereby saidamplifier 1mit is immersed in the gas which provides the acousticalcoupling for the amplifier unit with the result that heat produced bythe operation of said amplifier unit is transmitted to the surroundingcup walls and dissipated to atmosphere in an eflicient and dependablemanner.

MARC A. LALANDE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 814,411 Trowbridge Mar. 6, 1906975,933 Campbell Nov. 15, 1910 1,088,923 Pearson Mar, 3, 1914 1,306,248Clement June 10, 1919 1,622,507 Hahnemann et al. Mar. 29, 1927 1,683,946Baldwin Sept. 11, 1928 1,952,577 Bennett Mar. 27, 1934 2,080,837 ShraderMay 18, 1937 2,105,296 Pearson et al. Jan. 11, 1938 2,137,424 ThomasNov. 22, 1938 2,257,840 Dubilier Oct. 7, 1941

